It has long been recognized that control of a gas stream as the gas stream is introduced into a dust collecting apparatus can materially contribute to increased efficiency of operation and extended operating life of the gas treating components thereof. One area of preferential concern has been in the industrial gas filtration field, and particularly in the fabric filter dust collector field. One type of such fabric filter dust collector, also called a “baghouse”, typically employs a large number of tubular fabric filters suspended from a tube sheet and interposed in the path of a particulate-laden gas stream to effect the separation of the particulate matter from the gas. In essence, as the gas traverses the fabric filter media in its passage from the dirty air plenum to the clean air plenum portion of the filter housing, the filters trap the particulate matter on the outside of the bags. The clean gas then flows from the inside of the bags through outlets in the tube sheet and into an exhaust manifold.
In this type of dust collector, a particulate laden gas stream conventionally enters the filter housing through an upper sidewall portion of the collector housing defining at least a portion of the perimeter of the dirty air plenum. The particulate matter borne by the incoming gas stream normally accumulates on the outer surface of the bag and, unless removed by dislodgement, results in a progressive increase in pressure drop across the filter media and in a concomitant reduction in the rate of gas flow through the filter media. In order to avoid excessive particulate accumulation on the outer surface of the filter media, the filter media is periodically cleaned by utilization of various known techniques, such as by pulse jet or reverse flow cleaning or by bag shaking. The outcome of such a cleaning operation is that a large part of the accumulated particulates are induced to drop off the filter media surface and fall downwardly, under the influence of gravity, toward and into a collection hopper.
In most industrial fabric filter installations of the type described above, the particulate bearing gas stream approaches the filter through a delivery or conveying conduit having a cross-sectional area sized to effect gas stream displacement at sufficiently high velocities, usually in the order of 3500-4000 feet/min., to assure maintaining the particulate matter in suspended entrained condition therein. However, it has been recognized that high efficiency—low loss filter operation and increased operating life of the filter components is dependent, at least in substantial part, on an equable distribution of deposited particulates on all the available filter media surfaces; on minimization, if not avoidance, of turbulence in gas flow within the dirty air plenum; on minimization of particulate re-entrainment during or after filter media cleaning; and on minimization of localized wear and abrasion of filter components. As is apparent, a high velocity gas stream is basically antithetical to the desired optimum parameters of gas stream displacement within the filter housing. Reduction of the velocity of the air stream conventionally employs transition ducting and the interposition of turning vanes, baffle plates and related gas flow direction and velocity modifiers to the end of hopefully effecting a more equable distribution of the incoming gas steam relative to the available filter media surface and a marked reduction in its approach velocity.
In addition to the foregoing, achieving optimum operating parameters for the introduction of a particulate bearing gas stream into a dust collector is often complicated, if not effectively precluded, by physical restraints at the installation site. Among such physical restraints may be a less than adequate area for installation, the presence of duct work, piping, support columns, walls, catwalks and other impediments to ideal installation conditions.
The transition of the shape and velocity of the incoming particulate bearing gas stream to the desirable flow conditions within the fabric filter media housing has been a long-standing problem in this field. Many expedients, such as expansion of conduit dimension and the use of baffle plates, turning vanes, flow dividers, perforated plate diffusers, gratings, grids, various types of deflector or distribution plates and the selective location thereof in the path of the incoming gas stream and the like have been suggested to enhance performance in the separation and collection of industrial dusts. Illustrative of some of such varied expedients are U.S. Pat. Nos. 4,227,903; 4,544,383; 4,655,804; 4,213,766; 3,926,595; 3,831,354; 3,831,350; 3,739,557 and 3,425,189. While most of such expedients have resulted in some degree of improved performance, the net results have fallen far short of optimum and the problem of achieving high efficiency and economic operation of industrial fabric filter dust collectors remains a continuing one.
One proposed solution is described in U.S. Pat. No. 5,030,261 to Giusti, which discloses two different series of vanes that are arranged to confront the incoming airstream, tends to reduce the velocity of air entering the filter housing. Another solution is described in U.S. Pat. No. 4,799,943 to Giusti et al., which discusses a gas distribution apparatus comprising a series of concentric rings of increasingly smaller diameter that are spaced apart from each other along the flow path. These rings tend to distribute the air stream evenly across the length of the flow path. The disclosure of each of these patents is hereby incorporated by reference herein in its entirety.
Even with these solutions being offered, there still exists, for some facilities, the need for improved air flow characteristics.